1. Field of the Invention
This invention relates to rotation sensors, and more particularly to a rotation sensor and sensing method that utilizes the Coriolis effect.
2. Description of the Related Art
Devices currently used to measure rotation include Ring Laser Gyroscopes (RLGs) and Fiber Optic Gyroscopes (FOGs). RLGs and FOGs are based on the interference of two electromagnetic waves travelling in opposite directions within a closed optical loop. A rotation of the optical loop induces a phase difference between the two counter-propagating waves, which provides a measure of the rotation rate.
In a RLG, such as the one described in Anthony Lawrence, Modern Inertial Technology, Springer Verlag (1992), pp. 201-210, an active laser cavity is used as the sensing element. The cavity is pumped so that two counter-propagating electromagnetic waves are excited in the cavity. These waves optically interfere and produce a standing electromagnetic wave in the cavity. When the cavity is rotated with respect to inertial space, the standing wave rotates with respect to the RLG cavity. The differential motion between the RLG case and the standing wave produces a beat in the optical output of the cavity, with each beat representing a fixed measure of angular rotation.
Since the RLG is an active laser cavity, it must be carefully machined and precision optics must be used. In addition, the cavity must be purged of all contaminants and filled with a gain medium, such as a helium/neon gas mixture. These requirements make RLGs expensive and relatively large. Also, the RLG uses a large number of individual components (mirrors, anodes, cathodes, etc.), which reduce its operating life and reliability.
In a FOG, such as the one described in Anthony Lawrence, Modern Inertial Technology, Spinger Verlag (1992), pp. 183-188, the optical loop is formed from an optical fiber and the electromagnetic waves are provided by a solid-state laser. The optical fiber loop must be a precision-wound silica fiber coil. A phase modulator, optical coupler, polarizer and thermoelectric cooler are required. These components are spliced together in a highly precise fabrication process. The spliced components are packaged in another container to form the final assembled gyroscope. Like the RLG, the large number of components used in the FOG reduces its operating life and reliability. In addition, the highly precise fabrication process makes the FOG very expensive to manufacture.